Article of manufacture and method of making same



Jan. 22, 1963 D. M. YENNl ETAL 3,075,066

ARTICLE OF MANUFACTURE AND METHOD OF MAKING SAME Filed Dec. 3, 1957 2Sheets-Sheet l i v i25 Coafing 37 Ceramlc INVENTORS DONALD M, YENNIROBERT G. RUDNESS 3E5, Z M68 ATTORNE Jan. 22, 1963 D. M. YENNI ETAL3,075,066

ARTICLE OF MANUFACTURE AND METHOD OF MAKING SAME Filed Dec. 5, 1957 2Sheets-Sheet 2 Base Material INVENTORS DONALD M. YENNI ROBERT G. RUDNESSWWW ATTORNEY thereof.

Unite Stats atent 3,075,066 ARTICLE OF MANUFACTURE AND METHOD OF MAKINGSAME Donald M. Yenni and Robert G. Rudness, Indianapolis,

Ind., assignors to Union Carbide Corporation, a corporation of New YorkFiled Dec. 3, 1957, Ser. No. 700,363 8 Claims. (Cl. 219-46) Thisinvention relates to novel articles of manufacture containing electronemissive materials and methods of making them.

Briefly, according to the present invention, there is provided anentirely novel article of manufacture comprising the combination of anelectrically conductive material and at least one electron emissivematerial, said emissive material enabling the article to emit moreelectrons at a given temperature than does the pure electricallyconductive material. Such novel combination is fabricated byaccelerating and heating particles of the electrically conductivematerial and electron emissive material in a selected gas which ispassed through a high pressure electric arc and applied to a suitablesupporting member.

More particularly, according .to the invention, there is provided anovel article of manufacture composed of a body containing or coatedwith a mixture of refractory metal, such as chromium, niobium,molybdenum, nickel, tantalum, titanium, or tungsten, plus highlyemissive material, such as the emissive oxides calcia, ceria, baria,strontia, thoria, or yttria; fabricated by such are accelerated coatingprocess. In particular, novel bodies containing major amounts ofemissive metal oxide can be fabricated according to the presentinvention which could not be formed by any prior art methods known tous.

A specific novel modification of the present invention is an electrodecomposed of material such as tungsten which has a thin, dense, lamellaradherent coating of refractory metal plus emissive metal oxide.

Novel bodies of the invention are useful as welding electrodes, hotcathode emitters for electronic equipment, and are or sparkerosion-resistant electrodes.

The electron emissivity of welding electrodes and cathode emitters canbe increased by the incorporation therein of minor amounts of emissivematerials, such as metals, metal compounds and metal oxides, such asthoria, calcia, baria, yttria, strontia, ceria, and mixtures Bodiescontaining such emissive materials can be formed by slip-casting,sintering, and other powder metallurgy techniques. Sintered bodies areoften formed into finished shapes by swaging. As a general rule thehigher the emissive material content, the more difficult the swagingoperation. In commercial practice the upper limit for emissive oxide inswaged materials has been about by weight.

Novel bodies containing emissive materials, such as emissive metals,metal alloys and metal compounds such as metal oxides, having a broadcomposition range can be fabricated directly according to our inventionby the are accelerated plating process.

In the drawings:

FIG. 1 is a diagrammatic view of equipment illustrating the invention;

FIG. 2 is a view in side elevation of a ceramic base provided with atungsten-yttria coating that is shown in cross section;

FIG. 3 is a similar view of a stick electrode, the end portion of whichis provided with a tungsten-yttria coat- FIGS. 4-7 are views in crosssection and elevation of variously shaped bodies of the invention;

"ice

FIG. 8 is a view similar to FIG. 2 of an electronic member illustratingthe invention;

FIG. 9 is a photomicrograph of a cross section of body of the inventionin the as-formed condition;

FIG. 10 is a similar view of the prior art; and

FIG. 11 is a similar view of a body like that of FIG. 9 after heattreatment.

As shown in FIG. 1, the heat source comprises an arc torch I consistingof a central electrode 10 and a nozzle electrode 11 separated from eachother by an electrical insulator 12. Electrical supply 13, which can bedirect current-straight polarity, direct current-reverse polarity, oralternating current, is connected between electrodes 10 and 11 by lines14 and 15. Upon completion of such connection an are 16 is initiated.Selected torch gas stream 17 enters through inlet tube 18 and passes outthrough nozzle 11. An additional selected gas stream 19 enters the arctorch through tube 20. Coating material in the form of particles inhopper 21 drops in controlled amounts into gas stream 19 and the gasstream plus coating particles pass out through the nozzle electrode 11where they are heated by are 16. The gas stream is accelerated as itpasses out through the nozzle and thus accelerates the coating material.The accelerated and heated gas plus coating material form effiuent 22which impinges onto the workpiece 23 to deposit a coating 24. Theequipment shown is used to deposit a coating on a rotating support. Afiat surface or surface of other contour can also be coated bytraversing through the torch effluent.

The electrical connection 25 from power supply 13 to workpiece 23 isalternatively used when a transferred (work-in-circuit) arc is desired.An electrically conductive workpiece is necessary for this latterprocess.

The gas streams 17 and 19 are selected so as to be inert both to theworkpiece and thecoating material. In such way bodies of controlledcomposition can be formed. In particular, gases such as argon, helium,hydrogen and nitrogen are desirable. A reactive'gas, however, might beused, if desired, provided that the arc torch equipment is properlyprotected. p

A suitable base material can thus be coated with a mixture of refractorymetal plus emissive oxide or a refractory metal can receive a coating ofpure emissive oxide. The base material can be either an electricalconductor or non-conductor as desired.

The following examples describe the application of emissive coatings andoperational results of the coated product.

V Example I A coating 37, FIG. 12,- of tungsten-yttria was applied to aceramic base 38 'by passing 6.2 grams per minute tungsten powdercontaining 3 weight percent yttria suspended in a 50 c.f.h. argon streamthrough a nontrode in a high-frequency spark circuit and was operatedfor one hour without failure.

Example 2 A thin coating 39, FIG. 3, of tungsten-yttria was applied to afia-inch diameter pointed tungsten stick electrode 40 by passing6.0.grams per minute tungsten powder containing 10 weight percent yttriain a 50 c.f.h. argon carrier 3 gas stream through a non-transferred arctorch operating at 100 amps. and 53 volts. This gas-powder stream plus50 c.f.h. argon shielding gas passed out through the 7 inch diametertorch nozzle. Distance from torch nozzle to base material was /2 inch.

Such coated electrode was operated as an electric arc cathode up to 500amps. (DCSP) without melting. Uncoated pointed tungsten electrodesfailed under comparable conditions. Our procedure can also be used tocoat worn electrodes to rejuvenate their useful life.

An alternate procedure is to apply a coating onto a pattern and thenremove the pattern to form a shaped body having the desired composition.FIGS. 4-7 illustrate variously shaped bodies of the present inventioncontaining emissive metal oxides.

I The body 4 1 of FIG. 4 is hollow and is internally threaded at 42.FIG. 5 shows a body 43 of U-shape. The member 44 of FIG. 6 is tubular;as is member 45 of FIG. 7.. FIG. 8 illustrates an electronic member 46in which a coating 48 containing emissive metal oxide is applied to asupport 47 which is also a component part of the electronic member.

One of the advantages of using an are accelerated coating process forfabrication of such novel articles is the control obtained over thecoating composition. The are torch using an inert shielding gas is achemically inert heat source. Therefore the coating composition isdetermined primarily by the coating feed material minus any vaporizedmaterial. A coating or body of controlled varying composition can thusbe obtained. For example, pure tungsten can be applied as a coating.Gradually additional emissive oxide or oxides could be added to the feedmaterial and the tungsten content decreased. The resulting body formedcould thus have an increasing emissive oxide content along a radialdirection if so de sired. As another modification a coating containingemis- 's'ive material might only be applied to selected areas on thesurface of a support.

)7 Laminated articles of the present invention can also be fabricated byforming a coating or body of refractory metal, then alternately applyingcoatings of emissive metal oxide and refractory metals or mixturesthereof. 7 'l'he following table indicates the variety 'of materialswhich have been added to tungsten and applied as a coating according tothe invention. In addition to tungsten, other refractory metals can beused, such as molybdenum, nickel, chromium, niobium, tantalum, andtitanium.

TUNGSTEN COATINGS WITH VARIOUS ADDI-' The refractory metal-emissivematerial, such as metal oxide, coatings and formed bodies of the presentinvention have a characteristic lamellar microstructure in theiras-.formed, unswaged and non-drawn state composed irregularly shapedmicroscopic leaves overlapping and interlocking with each other. When amixture of refractory metal and emissivematerial is used, the resultingcoating or formed body of the present invention ghasa characteristicmicrostructure composed of irregularly shaped microscopic leaves ofemissive material dispersed among and interlocking with similarly shapedrn1croscopic leaves 'of refractory metal.

of such application.

FIG. 9 is a photomicrograph at 500 diameters magnification of a crosssection of a body of the present invention in the as-formed condition.The irregular shaped microscopic leaves 28 are the electricallyconductive material, such as tungsten. The irregular shaped microscopicleaves 29 interlocked therewith are the emissive metal oxide, such ayttria. Prior art bodies formed by slip-casting, sintering, powdermetallurgy and swaging techniques did not have this lamellarmicrostructure FlG. 10 shows a photornicrograph at 500 diametersmagnification of p a cross section of a prior art swaged tungstenelectrode containing minor amounts of emissive metal oxide. The tungstengrains 30 and the fibers of emissive oxide 31 are seen to be neitherlike microscopic leaves nor interlocking. Even though the chemicalcomposition may be similar, the articles of the present invention aretherefore characteristically. different in microstructure from knownprior art materials.

In addition, finished bodies of the present invention can have emissiveoxide content far above that of the prior art due to the are acceleratedfabrication technique which does not require swaging or drawing.

FIG. 11 shows a photomicrograph at 500 diameters magnification of across section of a body similar to that of FIG. 9 which has been heattreated to recrystallize the refractory metal and to change thedispersed emissive metal oxide into irregularly shaped nodules.

What is claimed is:

1. Process of making an electrode containing refractory metal andelectron emissive material which comprises accelerating and heatingparticles of said metal and emissive material in a non-swirling streamof selected gas which is passed through a high pressure electric are ata current of the order of 100 amperes and a potential of the order of 50volts, said accelerated and heated particles being then applied to asupporting member in a coherent mass.

2. Process of fabricating an electrode composed of refractory metal andmetal oxides, which comprises simultaneously discharging a stream ofinert gas, a high pressure arc, and a mixture of refractory metal andsubstantially uuvaporized but highly heated metal oxide particles as anextremely hot effluent from an electric arc torch, applying sucheflluent to a support until there is built up thereon a compositecomposed of microscopic lamellules of such particles that are welded oneto another without any change in the original purity of the refractorymetal and metal oxide constituting such particles by virtue of the inertvalue of such gas and the kinetic energy 3. Process of fabricating anelectrode composed of refractory metal and metal oxide, which comprisessimultaneously discharging a stream of inert gas and a mixture ofsubstantially unvaporized but highly heated refr'actory metal and metaloxide particles as an extremely hot efiiuent from an electric arc torchin which a high pressure are is drawn between the end of a centralelectrode and a nozzle-electrode surrounding such central electrode,applying such eflluent'to a support until there is built up thereon acomposite composed of microscopic lamellu'les of such particles that arewelded one to another without any change in the original purity of therefractory metal and metal oxide constituting such particles by virtueof the inert value of such gas and the kinetic energy of suchapplication.

4. Process as defined by claim 1, in which the ratio of refractory metalparticles to metal oxide particles is changed during the application ofthe mixture to vary the emissive and. conductive properties of theresulting composite.

5. Process of fabricating an electrode which comprises depositing alayer of emissive metal oxide on a support composed of refractory metalby applying to said support an extremely hot effluent comprising astream of inert gas and particles of said metal oxide which had8,075,066 5 6 been heated by a high pressure arc, said layer of metalReferences Cited in the file of this patent oxide consisting ofinterlocking and overlapping lamel- UNITED STATES PATENTS lules of metaloxide welded one to another and to said support, which lamellules are ofthe same purity as the 1,133,508 Schoop Mar. 30, 1915 originalparticles. 5 1,591,717 Marden July 6, 1926 6. Process of fabricating anelectrode which com- 1,952,854 Gehrts Mar. 27, 1934 prises depositingalternate layers of refractory metal and 2,172,207 Koll-igs et a1. Sept.5, 1939 emissive metal oxide to a suitable support by alternately2,204,391 Allen June 11, 1940 applying thereto an extremely hot effluentcomprising an 2,330,202 Brennan Sept. 28, 1943 inert gas stream andrefractory metal particles and an ex- 10 2,339,392 Garner Jan. 18, 1944trernely hot efiiuent comprising an inert gas stream and 2,353,635Aicher July 18, 1944 emissive metal oxide particles, said eifiuents eachhaving 2,361,378 Brennan Oct. 31, 1944 been heated by a high pressureelectric arc. 2,488,731 Lambert et a1 Nov. 22, 1949 7. An electrode madeaccording to the process of claim 2,700,000 Levi et a1. J an. 18, 19555, in which the support is a ceramic base. 15 2,754,225 Gfeller July 10,1956 8. An electrode made according to claim 5, in Which 2,768,279 RavaOct. 23, 1956 the support is composed of tungsten and the emissive2,775,531 Montgomery et al Dec. 25, 1956 oxide is selected from theclass consisting of thoria and 2,887,413 Ekkers et a1 May 19, 1959yttria. 2,903,544 Reichelt et a1 Sept. 8, 1959

1. PROCESS OF MAKING AN ELECTRODE CONTAINING REFRACTORY METAL AND ELECTRON EMISSIVE MATERIAL WHICH COMPRISES ACCELERATING AND HEATING PARTICLES OF SAID METAL AND EMISSIVE MATERIAL IN A NON-SWIRLING STREAM OF SELECTED GAS WHICH IS PASSED THROUGH A HIGH PRESSURE ELECTRIC ARC AT A CURRENT OF THE ORDER OF 100 AMPERES AND A POTENTIAL OF THE ORDER OF 50 VOLTS, SAID ACCELARATED AND HEATED PARTICLES BEING THEN APPLIED TO A SUPPORTING MEMBER IN A COHERENT MASS. 